1. Field of the Invention
The present invention relates to an exhaust heat recovery apparatus that recovers thermal energy from the exhaust gas of an internal combustion engine, factory exhaust heat, or the like to produce motive power.
2. Description of the Related Art
An exhaust heat recovery apparatus is available that, using a heat engine, recovers the exhaust heat from an internal combustion engine that is mounted on a vehicle, such as a passenger car, a bus and a truck. In the exhaust heat recovery apparatus used for such a purpose, an external combustion engine is used, such as the Stirling engine, which is excellent in theoretical thermal efficiency, for example.
Japanese Patent Application Publication No. 2004-332665 (JP-A-2004-332665) discloses a technology concerning a system that includes a combustion engine, an auxiliary, an electric generator, and a Stirling engine for driving the electric generator, wherein the electric power generated by the electric generator is supplied to a motor and a battery, and the auxiliary is driven by the motor, wherein, a clutch is provided between the auxiliary and the combustion engine, and the auxiliary is driven by the combustion engine or the motor in a selective manner using the clutch. In addition, Published Japanese Translation of PCT application No. 2003-518458 (JP-T-2003-518458) discloses a technology in which a clutch is provided between the internal combustion engine and the Stirling engine, and the Stirling engine is used as an additional drive unit of the internal combustion engine.
In the meantime, if the thermal energy recovered by the exhaust heat recovery unit is output as electric energy, the thermal energy recovered by the exhaust heat recovery unit declines because the energy conversion efficiency of motors and batteries is less than 100%. Moreover, the energy conversion efficiency of motors and batteries is less than the transmission efficiency achieved when a mechanical transmission means, such as gears and chains, is used.
In view of effective use of energy, as described in JP-T-2003-518458, it is preferable that the thermal energy recovered by the exhaust heat recovery unit be converted into kinetic energy to produce motive power, and the motive power produced by the exhaust heat recovery unit and the motive power produced by the heat engine be output after being combined using a mechanical transmission means.
In external combustion engines, such as the Stirling engine, the heat input from a heat source, such as the exhaust gas, is transferred to the working fluid of the external combustion engine through a heat exchanger, and external combustion engines are therefore less responsive to the variation of the heat input. In addition, external combustion engines, such as the Stirling engine, which obtain thermal energy from a heat source through a heater, sometimes continue to produce motive power even after the heat input is stopped, by virtue of the heat stored in the heater.
As a result, if an external combustion engine, such as the Stirling engine, is used as the exhaust heat recovery unit, the exhaust heat recovery unit sometimes continues to produce motive power by virtue of the heat stored in the heater that the exhaust heat recovery unit includes, even when exhaust heat is not supplied to the exhaust heat recovery unit. In such a case, in the case of the configuration in which the output from the exhaust heat recovery unit and the output from the heat engine are output together, the exhaust heat recovery unit produces surplus motive power even when there is no request to drive the heat engine.